1. Field of the Invention
This invention relates to apparatus for discharging an electrographic photoconductor as it moves along an endless path.
2. Description of the Prior Art
In a common form of electrographic copy/duplicator apparatus, an electrical image is formed on an electrographic photoconductor in response to image-wise actinic radiation from a document to be copied. The photoconductor includes a photoconductive layer with a conductive backing. Typically in the absence of light, the photoconductive layer accepts charge. When subject to light, the photoconductive layer becomes conductive and discharges through the conductive backing. In operation, the photoconductor is transported along an endless path relative to a plurality of work stations, each of which is operative when actuated to perform a work operation on the photoconductor.
Certain photoconductors, such as organic photoconductors exhibit a form of electrical fatigue that results in a "residual image" of a previous exposure being formed in initial copies of a new document.
This residual image or memory effect is believed to be caused by the accumulation of electrons trapped within the volume of the photoconductor in an image-wise pattern corresponding to the dark portion of the previous document image. The speed (rate of discharge per unit exposure) of the photoconductor is decreased by this accumulation of trapped electrons so that, upon exposure to a new document, the image area of the photoconductor associated with the previous document pattern is discharged less than other photoconductor portions and is developed with toner as a background image. It will be readily appreciated that such a background image is detractive from an esthetic viewpoint; and, the provision of previous document information in the subsequent document copies may present a serious problem when proprietary information is embodied in the previous document.
It is well known that fatigue of the type causing the residual image effect in photoconductors can be relieved to some extent by discharging such photoconductors by, flooding them with light or by heating, them (see for example U.S. Pat. No. 2,863,767 and Electrophotography by R. M. Schaffert, 2nd Edition, 1975, page 167). Typically this is accomplished just after the development station and before any subsequent sensitizing or charging of the photoconductor. It is also quite common practice to discharge a photoconductor by flooding light on it just prior to cleaning. This not only aids in cleaning but also conditions the photoconductor for primary charging or sensitizing.
The spectral characteristics of the photoconductor, of course, depend upon its particular construction. For the sake of illustration let us assume that to effectively discharge a particular photoconductor, it's spectral characteristics are such that, preferably, it should be illuminated with light having a substantial component of "red" visible light. In order to discharge an organic photoconductor special purpose commerically available fluorescent lamps are frequently employed. For example, a Sylvania, F17 1/4 T5/RS lamp has been mounted using conventional electrical components in proximity to the back of a transparent organic photoconductor. A suitable refector surrounds the portion of the lamp not facing the photoconductor to maximize the light incident on the photoconductor. While such special purpose fluorescent lamps can perform satisfactorily, they typically have a limited life, have a relatively high cost and provide light which does not precisely match the spectral characteristics of the photoconductor and thus waste energy. Heretofore when it was desired to discharge a photoconductor both after development and prior to sensitizing, two special purpose fluorescent lamps were provided.